Cruciferous vegetable plants (such as Brassica plants like broccoli) accumulate 4-methylsulphinylbutyl glucosinolate (glucoraphanin) and 3-methylsulphinylbutyl glucosinolate (glucoiberin). These glucosinolates are hydrolysed to isothiocyanates. Epidemiological studies correlate diets rich in cruciferous vegetables with a reduction in a risk of cancer. High glucosinolate Cruciferous vegetables (e.g. high glucosinolate broccoli) have been developed as described in WO99/52345 and PCT/GB2009/001648. The production of glucosinolates in Cruciferous vegetable plants is complex as can be seen from the map of sulphur flux in plants shown in FIG. 4. Prior to the present invention methylthioalkylmalate synthase (MAM) metabolic or molecular markers were used in breeding programs. It was known that MAM1 and MAM3 closely associated with high glucosinolate traits.
The present inventors surprisingly observed that some Brassica cultivars with high glucosinolate (e.g. glucoraphanin) phenotype did not possess the MAM marker alleles though to be associated with the trait, thus concluding that the MAM markers were not necessarily closely linked to or the key to the high glucosinolate profile and therefore their use as markers in breeding was not reliable for the tracking of this trait.
The inventors therefore sought a marker for high glucosinolates which could be reliably and consistently used to determine the genotype of a plant with an increased glucosinolate level.